In a previously-proposed data storage device, data is stored on a storage medium along Track Center Lines (TCLs) of the data storage device. The data is read/written by moving each read-head along a TCL of a data-track relative to the storage medium. The data may be read/written by moving the storage medium relative to each read head, such that each read head moves along a TCL of a data-track. However, it may be that a read-head may be moved along a line that has an offset from a TCL of a data-track. A PES corresponding to a position of read-heads is obtained for the data storage device when the data is read/written. The PES is converted into a position offset of each read-head from a TCL of a data-track. The position offset is used to move each read-head on a TCL of a data-track.
In a previously-proposed data storage device, for example, a hard disk device, PES is generated based on read-back signals obtained by scanning corresponding servo-bursts on a storage medium. Servo-bursts are magnetic fields that are pre-written on the storage medium during manufacturing of a hard disk drive. In one possible configuration, the servo-bursts are positioned off-track with data-tracks such that, a TCL of a data-track coincides with a boundary of a servo-burst. Further, a servo-burst, a data-track and a read-head have comparable cross-track widths. Therefore, when a read-head moves on a TCL of a data-track, equal portions of a first servo-burst and a second servo-burst are scanned by the read-head. Boundaries of the first servo-burst and the second servo-burst coincide with a TCL of the data-track.
The read head obtains a first read-back signal from a first servo-burst and a second read-back signal from a second servo-burst. The first read-back signal is zero if the read-head is entirely placed on the second servo-burst. Similarly, the second read-back signal is zero if the read-head is entirely placed on the first servo-burst. Thereafter, the PES is obtained by dividing the difference of the first read-back signal and the second read-back signal by the sum of the first read-back signal and the second read-back signal. The sum of the first read-back signal and the second read-back signal is constant as the read-head has a cross-track width comparable to each of data-track, the first servo-burst, and the second servo-burst.
However, in probe based data storage devices, a width of a read-head is considerably smaller than a width of a servo-burst and a data-track and data is written as a plurality of topographical features. Examples of the topographical features may include, but are not limited to indentations, trenches, and bumps. Therefore, the method used for calculating PES in hard disk drives is not effective in probe based data storage devices. This is because the sum of the first read-back signal and the second read-back signal is not constant across the entire cross-track distance between adjacent tracks.
The PES for a probe based data storage device can be calculated using the method of calculating PES in hard disk drives provided a constant sum for the first read-back signal corresponding to the first servo-burst and the second read-back signal corresponding to the second-burst can be obtained. The constant sum can be obtained by placing a topographical feature of the first servo-burst at a predefined distance from a corresponding topographical feature of the second servo-burst.
However, placing a topographical feature of the first servo-burst at a predefined distance from a corresponding topographical feature of the second servo-burst usually leads to partial erasing of the topographical features. Additionally, tips of the read-heads wear down and the topographical features tend to change shape with time. This leads to a distortion in the read-back signals over time.